To a solution of (3R,4S,5S)-3-amino-5-[3-fluoro-4-nitro-5-((R)-2,2,2-trifluoro-1-methoxy-methyl-ethoxy)-benzyl]-tetrahydro-thiopyran-4-ol hydrochloride (1.217 g, 2.52 mmol) in MeOH-CH2Cl2 1:2 (28 mL) was added NaOAc (0.517 g, 6.3 mmol), powdered molecular sieves (4A) and 3-tert-butyl-benzaldehyde (CAS registry 23039-28-3) (0.413 g, 2.55 mmol). The reaction mixture was stirred at 25° C. for 16 h, acetic acid (0.5 mL) was added followed by NaBH3CN (0.396 g, 6.3 mmol). The reaction mixture was stirred at room temperature for 3 h and was quenched by adding 2N aq. HCl solution. EtOAc was added and the solution was washed with 2N K2CO3 solution and with brine. The organic phase was dried over Na2SO4, filtered and evaporated. The title compound was obtained after purification by flash-chromatography on NH4OH deactivated silica gel (90 g, toluene-EtOAc 1:1) as a light yellow oil: TLC (toluene-ETA 85:15) Rf=0.52; HPLC RtA=2.178 min; ESIMS [M+H]+=575; 1H NMR (600 MHz, CDCl3): δ 7.33 (s, 1H), 7.28 (s, 1H), 7.26 (m, 2H), 7.18-7.08 (m, 2H), 5.7 (broad, 1H), 5.06 (d, 1H), 3.9-3.78 (m, 2H), 3.71-3.62 (m, 2H), 3.31 (s, 3H), 3.22 (d, 1H), 2.90 (m, 1H), 2.82 (d, 1H), 2.55 (m, 1H), 2.48 (s broad, 1H), 2.41 (m, 1H), 2.35-2.20 (m, 3H), 1.93 (m, 1H), 1.25 (s, 9H).
